Chapter 47 Discontinuing Ventilatory Support

1. Chapter 47Discontinuing Ventilatory Support

2. Learning Objectives • Discuss the relationship between ventilatory demand and ventilatory capacity in the context of ventilator discontinuance. • List factors associated with ventilator dependence. • Explain how to evaluate a patient before attempting ventilator discontinuation or weaning. • List acceptable values for specific weaning indices used to predict a patient’s readiness for discontinuation of ventilatory support. • Describe factors that should be optimized before an attempt is made at ventilator discontinuation or weaning.

3. Learning Objectives (cont.) • Describe techniques used in ventilator weaning, including daily spontaneous breathing trials, synchronized intermittent mandatory ventilation, pressure support ventilation, and other newer methods. • Contrast the advantages and disadvantages associated with various weaning methods and techniques. • Describe how to assess a patient for extubation. • List the primary reasons why patients fail a ventilator discontinuance trial. • Explain why some patients cannot be successfully weaned from ventilatory support.

4. Introduction • Ventilatory support sustains life but is not curative • Has many complications and hazards • Should be withdrawn expeditiously • All patients should be evaluated on a daily basis for their ability to wean from ventilatory support • Balance desire for early extubation with its exposure to the risks of reintubation.

5. Ventilatory Capacity

6. All of the following are TRUE about mechanical ventilation, except: • Ventilatory support sustains life but is not curative. • It has few complications and hazards. • It should be withdrawn expeditiously. • All patients should be evaluated on a daily basis for their ability to wean from ventilatory support

7. Methods of Discontinuing Ventilation • Three main methods • Spontaneous breathing trials (SBT) • SIMV • PSV • Novel modes with no data to support • VSV = volume support ventilation, MMV= mandatory minute volume ventilation, ATC = automatic tube compensation, PAV = proportional assist ventilation **Systematic review: 1 SBT per day has shown best results

8. Probability of Successful Weaning

9. Discontinuing Ventilatory Support • In general, patients being considered for removal from ventilatory support fall into one of four categories: • removal is quick and routine, normally the vast majority of patients • need a more systematic approach, about 15 to 20% of ventilated patients • require days to weeks to wean, usually less than 5% of patients • ventilator-dependent or “unweanable” patients, less than 1% of patients

10. Global Criteria for Discontinuing Ventilatory Support(cont.) • Success is tied to • Ventilatory work load versus capacity • Oxygenation status • Cardiovascular status • Psychological factors

11. Most Important Criteria • Reversal of disease state that necessitated ventilatory support • Oxygenation status adequate on <0.5 FIO2 • Medically and hemodynamically stable • Patient can breathe spontaneously • If the above are all true, then perform a formal evaluation for extubation.

12. 66 Measurements: 8 Most Consistently Predictive • Spontaneous rate 6 to 30 beats/min • Spontaneous VT >5 ml/kg • f/VT (RSBI) – most predictive <105 • Minute ventilation <10 L/min • MIP <20 to 30 mm Hg • P0.1 <6 cm H2O • P0.1/MIP <0.3 • CROP (CDyn, f, O2, PImax) >13 * No single index has high predictive power, so it is important to consider the total picture.

13. Which of the following predictive value is consistent with a patient weaning successfully? • Spontaneous rate 40 beats/min • Spontaneous VT 4 mL/kg • f/VT (RSBI) 85 • MIP –18 mm Hg

14. Preparing the Patient • Patient should be rested and stable • Maximize bronchodilator and anti-inflammatory medications as well as bronchial hygiene • Communicate well with patient so as to relieve/minimize anxiety • Optimize nutrition, acid/base status, fluid balance, and oxygenation • Minimize sedation

15. Rapid Ventilator Discontinuance • Patients that are likely to wean rapidly • Presenting problem corrected in 72 hours • Good weaning parameters • Good results in SBT of 30 to 120 minutes • If the above criteria are met, most patients can be removed from ventilatory support • If the patient can protect his or her airway, then extubate at this time

16. Progressive Weaning of Ventilatory Support • Patients likely to need longer weaning period • Ventilated longer then 72 hours • Marginal: oxygen, ventilatory, cardiovascular, or medical status • Most common methods of weaning: • SBT alternating with rest periods on • A/C, SIMV, or significant levels of PSV

17. Progressive Weaning: SBT • T-tube trial • 5 to 30 minutes SBT • 1 to 4 hours of rest on A/C, SIMV, or high PSV • Gradually, SBT times increase while rest periods diminish • Patients rested at night • Alternate method is 1 SBT/day and then rest. • This can also be done on the ventilator in CPAP mode with PSV or ATC.

18. Initial Screening SBT • Perform 2–3 minute SBT. If 2 out of 3 of the criteria below are met, start formal wean • VT >5 ml/kg • RR <30–35 beats/min • MIP-a.k.a (NIF) <20 cm H2O • Alternate: adequate cough, no vasopressors • P/F ratio >200 • PEEP 5 • f/VT <105

19. SBT Termination • Termination occurs if any of these criteria met • Agitation, anxiety, diaphoresis, altered mental state • Respiratory rate > 30 or 35 beats/min • SpO2 <90% • 20% change in HR or HR > 120 to 140 beats/min • Systolic BP > 180 mm Hg or < 90 mm Hg

20. Weaning With SIMV • Faster weans claimed but contrary to evidence • Ease of use is primary reason for use • Evidence that at 50% of full ventilatory support, patient WOB approximates that on CPAP • In addition, demand flow SIMV imposes considerable WOB • Modern ventilators minimize this effect.

21. Weaning With SIMV (cont.) • Support set below required level; patient makes up the difference. • Once precipitating event corrects, support is rapidly reduced. • Support is typically reduced in increments of 2 breaths per minute until spontaneous ventilation is achieved

22. All of the following are TRUE about SIMV weaning except: • Faster weans claims are supported by evidence • Ease of use is primary reason for use • Evidence that at 50% of full ventilatory support, patient WOB approximates that on CPAP • Demand flow SIMV imposes considerable WOB

23. PSV Weaning • Level is set to PSVmax 6 to 10 ml/kg. • On resolution of precipitating event • PSV reduced increments 2 to 4 cm H2O, usually 1 to 2 times per day • Rested at nights • 2 strategies for discontinuance of PSV: • Patient tolerates PSV of 5 – 8 cm H2O with no distress • Patient tolerates CPAP with no PSV without distress

24. Monitoring During Weaning • PaCO2 best index of adequacy of ventilation but only tied to clinical data • PaCO2 40 mm Hg with f/VT of 250 shows impending ventilatory failure. • PaCO2 40 mm Hg with f/VT of 40 shows ability to breathe spontaneously. • SpO2 monitor continuously • Cardiovascular status

25. Extubation • Weaning and extubation separate decisions • Extubation requires • Ability to protect airway • Gag • Effective cough • Airway patency • Minimal edema • Positive “cuff-leak” > 12% volume loss • Adequate pulmonary hygiene

26. All of the following are required for extubation, except: • Maximal edema • Patients ability to protect airway • Airway patency • Adequate pulmonary hygiene

27. Postextubation Stridor • Occurs in 2% to 16% of ICU patients • Can result in complete airway obstruction • Management includes • Cool aerosol mist with oxygen via mask • Nebulized racemic epinephrine (0.5 ml 2.25%) • Nebulized 1 mg in 4 ml NS dexamethasone • HeliOx 60%/40%

28. Failure of Extubation • Up to 25% of patients require MV again • Half of patients with distress following MV discontinuance develop marked hypercapnia • Myocardial ischemia associated with failed weaning attempts • Failed weans may be undiagnosed NMD or psychological dependence • Most common reason: inadequate ventilatory capability which cannot meet ventilatory demand

29. Chronically Ventilator-Dependent Patients • Prolonged MV occurs in 3% to 7% of ventilated patients, while <1% become dependent • Definition: ventilator dependency remains following 3 months of weaning attempts • Special long-term acute care facilities specialize in weaning these patients • Once dependency established, goal is to restore highest level of independence

30. Terminal Weaning • Refers to weaning in the face of catastrophic and irreversible illness • Weaning occurs despite likely result of patient death • Decision made by patient and/or family in consultation with physician. • Must meet ethical and legal guidelines • May be due to advanced directives, current patient decision, or very poor prognosis